Method of Producing Hollow Silica Microparticles

ABSTRACT

A method of producing hollow silica microparticles that suppress whitening of a transparent coating film and show excellent abrasion resistance and adhesiveness. The method includes preparation of an organosol in which hollow silica microparticles are dispersed with the silica concentration of 1 to 70 W % and addition of a silane compound and an alkali catalyst to the organosol at a temperature in the range from 30° C. to 300° C. to react the silane compound to the hollow silica microparticles under the condition where a quantity of water against the added silica (the hollow silica microparticles) is in the range from 0.1 to 50 W %.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of Ser. No. 12/085,367 filed on May 22,2008.

The present invention relates to a method of producing the hollow silicamicroparticles. The hollow silica microparticles having a surfaceprocessed with a silane compound, compositions for forming a transparentcoating film containing the hollow silica microparticles, and asubstrate having a surface coated with a transparent coating filmprepare by curing the composition for forming a transparent coating filmare also described.

BACKGROUND TECHNOLOGY

Hollow silica particles with the diameter of about 0.1 to about 380 μmare well known (Refer to Patent document 1 and Patent document 2).Furthermore, there has been known the method of producing hollowparticles having a hard silica shell in which active silica is depositedfrom an aqueous solution of alkali metal silicate on a core made of amaterial other than silica, and the material is removed without breakingthe silica shell (Refer to Patent document 3).

Furthermore, there has been known the micron-sized spherical silicaparticles having the core shell structure in which the externalspherical surface is a shell, the central portion thereof is hollow, andthe shell has a density gradient from the dense outer side toward thethin inner side (Refer to Patent document 4).

The present applicant proposed in the past to obtain composite oxidemicroparticles with a low refractive index and also having the size at alevel of nanometers by completely coating surfaces of porous inorganicmicroparticles with such materials as silica (Refer to Patent document5), and furthermore proposed to obtain silica-based hollowmicroparticles with a low refractive index and having the size at alevel of nanometers by forming a silica coating layer on core particlesof composite oxides comprising silica and inorganic oxides other thansilica, removing the inorganic oxides other than silica, and coating theparticles with silica (Refer to Patent document 6).

Furthermore, addition of spherical microparticles to an organic resinfilm is a known technique, and there has been known the fact that, withthe technique, transparency of the obtained film is improved (Refer toPatent document 7).

In the films containing the silica particles or the transparent coatingfilms as described above, there often occurs the problem that theobtained films or the transparent coating films are whitened.

Paten document 8 includes descriptions concerning the fact that, incompositions for coating containing (a) a partial condensate of anorganic silicon compound comprising 100 weight portions oftrialkoxysilane expressed by general formula: RSi(OR₁)₃ [R: ahydrocarbon group containing 1 to 6 carbon atoms, R₁: an alkyl groupcontaining 1 to 6 carbon atoms] and 20 to 130 weight portions oftetraalkoxysilane expressed by the general formula of Si(OR₂)₄ [R₂: analkyl group containing 1 to 6 carbon atoms; and (b) 0.05 to 200 weightportions of silica microparticles against 100 weight portions of thepartial condensate (RSiO_(3/2)+SiO₂) when the trialkoxysilane iscalculated as RSiO_(3/2) and the tetraalkoxysilane as SiO₂, whitening ofthe coating film can be suppressed by limiting a blending quantity ofsilica microparticles.

Patent document 9 proposes a method of using the inorganic compoundparticles with the average particle diameter of 50 nm or below forpreventing whitening of a transparent coating film obtained by applyingan embrocation for forming a transparent coating film in which (A) aacetylacetonato-chelate compound and (B) inorganic compoundmicroparticles are homogeneously dissolved or dispersed in a mixturesolvent of water and an organic solvent to a base material and curingthe embrocation.

Patent document 10 proposes a reflection-preventive film with thesurface hardly damaged by frictions or the like and also with the lowrefractive index layer not separated, and the reflection-preventive filmhas a hard coat layer based on a UV cure resin mainly made of amultifunctional monomer containing two or more (metha) acryloyloxygroups in the molecule with inorganic microparticles having the averageparticle diameter of 0.5 to 100 nm added in the matrix, the hard coatlayer formed on at least one surface of a transparent plastic filmsubstrate, and a low refractive index layer formed on the hard coatlayer and based on a matrix made of a copolymer of an organic siliconcompound or a polymer thereof and an organic silicon compound or apolymer thereof with silica microparticles having the average particlediameter of 0.5 to 100 nm added therein, and the document also describesthat, when using the inorganic microparticles with the average particlediameter of less than 20 nm, whitening of the hard coat layer due toscattering of light can be prevented.

As a transparent coating film containing hollow silica microparticlesand an embrocation for forming the transparent coating film, forinstance, Patent document 11 discloses an invention relating to atransparent film-coated substrate formed thereon, and the substratecomprises a base material and a transparent coating film provided on asurface of the substrate, and the transparent coating film has (i) amatrix containing a silicon component in turn containing afluorine-substituted alkyl group and (ii) an outer shell layer, and alsocontains inorganic compound particles which are porous or have manycavities therein. The transparent coating film is also characterizedthat the porosity or the cavities are preserved therein. In thetransparent coating film containing hollow silica microparticles and abinder as described above, however, although the low refractive index ofabout 1.25 to about 1.45 specific to the hollow silica microparticlescan be realized, whitening of the coating film easily occurs, and thereis the need for further improving the adhesiveness to the base materialand the abrasion resistance.

Patent document 1: JP H06-330606A

Patent document 2: JP H07-013137A

Patent document 3: JP 2000-500113A

Patent document 4: JP H11-029318A

Patent document 5: JP H07-133105A

Patent document 6: JP 2001-233611A

Patent document 7: JP H04-348147A

Patent document 8: JP H01-306476A

Patent document 9: JP H04-247427A

Patent document 10: JP 2004-326100A

Patent document 11: JP 2002-79616A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

When a coating composition containing hollow silica microparticles and abinder is prepared and a transparent coating film is formed on asubstrate using the coating composition, a transparent coating filmhaving a lower refractive index as compared to that when a compositioncontaining ordinary silica microparticles and a binder is prepared and atransparent coating film is formed by using the composition, but whenhollow silica microparticles are used, whitening more easily occurs inthe transparent coating film, which is disadvantageous, and in addition,there is also the need for further improving the abrasion resistance andadhesiveness.

The present invention was made to solve the problems as described above,and it is an object of the present invention to provide hollow silicamicroparticles capable of suppressing, even when a coating compositioncontaining hollow silica microparticles and a binder is prepared and atransparent coating film is formed on a substrate, whitening of thetransparent coating film and showing the excellent abrasion resistanceand the adhesiveness and also to provide a method of producing thehollow silica microparticles. It is another object of the presentinvention to provide compositions for forming a transparent coating filmcontaining the hollow silica microparticles showing the excellenteffects as described above and a transparent film-coated substrateobtained by curing the composition for forming a transparent coatingfilm.

It is another object of the present invention to provide a transparentfilm-coated substrate in which hollow silica microparticles are unevenlydistributed in the layer state, and compositions for forming atransparent coating film to produce the substrate as described above. Itis still another object of the present invention to provide atransparent film-coated substrate in which hollow silica microparticlesand metal oxide microparticles are unevenly distributed in the layeredstate respectively and compositions for forming a transparent coatingfilm to produce the substrate as described above.

Means for Solving the Problems

The present invention provides, in a first aspect thereof, hollow silicamicroparticles having the average particle diameter of 5 to 300 nm whenmeasured by the dynamic light scattering method, and the specificsurface area of 50 to 1500 m²/g, and also having an outer shell in whichcavities are formed, and the hollow silica microparticles lose theweight by 1.0 W % (weight %) or more at a temperature range from 200° C.to 500° C. when measured by the thermogravimetry (TG).

The present invention is characterized in a second aspect thereof inthat the hollow silica microparticles have a positive DTA peak at atemperature in the range from 200° C. to 500° C. when measured by thedifferential thermogravimetric analysis (DTA).

The present invention is characterized in a third aspect thereof in thatthe hollow silica microparticles have an organic group directly bondedto a silicon atom on a surface thereof.

The present invention is characterized in a fourth aspect thereof inthat the hollow silica microparticles has an organic group directlybonded to a silicon atom on a surface thereof and the organic group isone or more selected from the group consisting of saturated orunsaturated hydrocarbon groups having 1 to 18 carbon atoms andhalogenated hydrocarbon groups having 1 to 18 carbon atoms.

The present invention provides, in a fifth aspect thereof, a method ofproducing hollow silica microparticles comprising the steps of preparingan organosol with the silica concentration of 1 to 70 W % in whichhollow silica microparticles are dispersed; and adding a silane compoundand an alkali catalyst to the organosol at a temperature in the rangefrom 30° C. to 300° C. to react the silane compound to the hollow silicamicroparticles under the condition that a quantity of water against theadded silica (the hollow silica microparticles) is in the range from 0.1to 50 W %.

The preset invention provides, in a sixth aspect thereof, a method ofproducing hollow silica microparticles in which a quantity of addedsilane compound is in the range from 1 to 50 weight portions against 100weight portions of the hollow silica microparticles and a quantity ofadded alkali catalyst is in the range from 20 to 2,000 ppm against theorganosol.

The present invention provides, in a seventh aspect thereof,compositions for forming a transparent coating film in which hollowsilica microparticles relating to any of the first to fourth aspects ofthe present invention and a binder are contained.

The present invention provides, in an eighth aspect thereof, a substratehaving a surface coated with a transparent coating film prepared bycuring the composition for forming a transparent coating film relatingto the seventh aspect of the present invention.

The present invention provides, in a ninth aspect thereof, the hollowsilica microparticles in the fourth aspect, and the hollow silicamicroparticles are furthermore characterized in that the microparticleshave the organic group expressed by general formula (1) or (2) and losethe weight by 1.5 W % or more at a temperature in the range from 200° C.to 500° C. when measured by thermogravimetry (TG).

—R—OC(═O)CCH₃═CH₂  General formula (1):

(R: A bivalent hydrocarbon group having 1 to 12 carbon atoms)

—R—OC(═O)CH═CH₂  General formula (2):

(R: A bivalent hydrocarbon group having 1 to 12 carbon atoms)

The present invention provides, in a tenth aspect, the hollow silicamicroparticles in the fourth aspect, but the hollow silicamicroparticles have the organic group expressed by general formula (3):

—R—C_(n)F_(a)H_(b)  General formula (3):

(a+b=2n+1, n is an integer of 1 to 3, while R is a bivalent hydrocarbongroup having 1 to 12 carbon atoms).

The present invention provides, in an eleventh aspect thereof,compositions for forming a transparent coating film in which a surfacecharge (Q_(A)) of the hollow silica microparticles contained in thecomposition for forming the transparent coating film relating to theseventh aspect of the present invention is in the range from 5 to 20eq/g.

The present invention provides, in a twelfth aspect thereof, compositionfor forming a transparent coating film in which a concentration (C_(PA))of the hollow silica microparticles contained in the compositionrelating to the eleventh aspect of the present invention is in the rangefrom 0.1 to 20 W %, a concentration (C_(M)) of the binder as a solid isin the range from 1 to 50 W %, and the solvent is a polar solvent.

The present invention provides, in a thirteenth aspect thereof,compositions for forming a transparent coating film relating to theseventh aspect of the present invention in which hollow silicamicroparticles with the surface charge (Q_(A)) in the range from 5 to 20μeq/g are contained, also metal oxide microparticles with the surfacecharge (Q_(B)) in the range from 51 to 150 μeq/g are contained, and avalue of the difference between the surface charge (Q_(B)) of the metaloxide microparticles and that (Q_(A)) of the hollow silicamicroparticles [(Q_(B))−(Q_(A))] is in the range from 20 to 100 μeq/g.

The present invention provides, in a fourteenth aspect thereof,compositions for forming a transparent coating film in which aconcentration (C_(PA)) of the hollow silica microparticles contained inthe compositions relating to the thirteenth aspect of the presentinvention is in the range from 0.1 to 20 W %, a concentration (C_(PB))of the metal oxide microparticles is in the range from 0.1 to 20 W %,and a concentration (C_(M)) of the binder as a solid is in the rangefrom 1 to 50 W %, and a solvent thereof is a polar one.

The present invention provides, in a fifteenth aspect thereof, asubstrate having a surface coated with a transparent coating film (withthe thickness of 100 nm to 10000 nm) prepared by curing the compositionfor forming a transparent coating film relating to the eleventh ortwelfth aspect of the present invention, in which the hollow silicamicroparticles are unevenly distributed and dispersed in the outer sideof the surface from the middle point in the thickness direction of thetransparent coating film.

The present invention provides, in a sixteenth aspect thereof, thetransparent film-coated substrate relating to the fifteenth aspect, inwhich the hollow silica microparticles are unevenly distributed anddispersed in the single-layered or multilayered state.

The present invention provides, in a seventeenth aspect thereof, asubstrate having a surface coated with the transparent substrate (withthe thickness of 100 nm to 10000 nm) prepared by curing the compositionfor forming a transparent coating film relating to the thirteenth orfourteenth aspect of the present invention, in which the hollow silicamicroparticles are unevenly distributed and dispersed in the surfaceside outer from the middle point in the thickness direction of thetransparent coating film and the metal oxide microparticles are unevenlydistributed and dispersed in the substrate side inner from the middlepoint in the thickness direction of the film.

The present invention provides, in an eighth aspect thereof, thetransparent film-coated substrate relating to the seventeenth aspect, inwhich the hollow silica microparticles are unevenly distributed anddispersed in the single-layered or multilayered state and the metaloxide microparticles are also unevenly distributed and distributed inthe single-layered or multilayered state.

The present invention provides, in a nineteenth aspect thereof, hollowsilica microparticles with the average particle diameter of 5 to 300 nmwhen measured by the dynamic light scattering method, and the specificsurface area of 50 to 1500 m²/g and having an outer shell in whichcavities are formed, and the hollow silica microparticles lose theweight by 1.0 W % or more at a temperature in the range from 200° C. to500° C. when measured by the thermogravimetry (TG), have a positive DTApeak at the temperature range when measured by the differentialthermogravimetric analysis (DTA), have an organic group directly bondedto a silicon atom on a surface thereof, and also have a surface charge(Q_(A)) in the range from 5 to 20 μeq/g.

The present invention provides, in a twentieth aspect thereof, a methodof producing hollow silica microparticles comprising the steps ofpreparing an organosol with the concentration of silica in the hollowsilica microparticles in the range from 1 to 70 W %, and adding a silanecompound and/or a multifunctional acrylic acid ester resin having ahydrophobic functional group, and an alkali catalyst to react the silanecompound to the hollow silica microparticles in the state where aquantity of water against the added silica is in the range from 0.1 to50 W %.

Effects of the Invention

The transparent coating film obtained by applying the compositions forforming a transparent coating film containing hollow silicamicroparticles and a binder according to the present invention has a lowrefractive index in the range from 1.25 to 1.45, and discoloring such aswhitening hardly occurs in the compositions, and the compositions areexcellent in the abrasion resistance and the adhesiveness. Furthermorethe transparent coating film is also excellent in the chemicalresistance and the water resistance, and for instance, when waterdroplets dropped on a surface of the transparent coating film accordingto the present invention are wiped off, advantageously no trace of thedroplets is left.

With the production method according to the present invention, thehollow silica microparticles can efficiently be produced.

Of the substrates each with a transparent coating film according to thepresent invention, especially those having a transparent coating film inwhich a specific quantity of hollow silica microparticles are unevenlydistributed in the layer state show the excellent characteristics basedon the hollow silica microparticles (such as the capability ofsuppressing reflection and the antistatic property). Furthermore, in thetransparent film-coated substrate according to the present invention,when prespecified hollow silica microparticles and prespecified metaloxide microparticles are unevenly distributed in the layered staterespectively, in addition to the characteristics provided by the hollowsilica microparticles, also the characteristics based on the metal oxidemicroparticles are easily and strongly shown. Especially, with thecompositions for forming a transparent coating film according to thepresent invention in which prespecified hollow silica microparticles andprespecified metal oxide microparticles are contained, it is possible toobtain a transparent coating film in which hollow silica microparticlesand metal oxide microparticles are unevenly distributed in the layeredstate respectively or a substrate having the transparent coating film.

BEST MODE FOR CARRYING OUT THE INVENTION [Hollow Silica Microparticles]

The hollow silica microparticles according to the present invention havean outer shell with cavities formed therein and also have an averageparticle diameter of 5 to 300 nm and a specific surface area of 50 to1500 m²/g, and lose the weight by 1.0 W % or more at a temperature inthe range from 200° C. to 500° C. when measured by the thermogravimetry(TG). The hollow silica microparticles generally show a positive DTApeak when measured by the differential thermogravimetrical analysis at atemperature from 200° C. to 500° C.

The hollow silica microparticles according to the present invention aregenerally prepared by subjecting known hollow silica microparticles to asurface processing with a silane compound. More specifically, because ofa hydrolysis reaction between a silanol group on a surface of the hollowsilica microparticles and the silane compound, an organosilyl group(monoorganosilyl, diorganosilyl, or triorganosilyl group) directly bondsto a surface of the hollow silica microparticles, and the hollow silicamicroparticles according to the present invention have a number oforgano silyl groups each directly bonding to a silicon atom on a surfacethereof.

It is generally said that the organic group as described above bonds toa surface of the hollow silica microparticle with a structure likeSi—O—SiA₃ (A: an organic group) through the reaction between the silanecompound and the silanol group on a surface of the hollow silicamicroparticle.

The thermogravimetric analysis is performed to measure a change in aweight of a sample due to up and down of the atmospheric temperaturearound the sample, and the change showing a change in a weight againstthat in a temperature is called TG curve. The differentialthermogravimetric analysis is performed to measure a calorimetric changeagainst a change in a temperature by detecting a difference between atemperature of a reference and that of a sample making use of a anelectromotive force of a thermocouple provided in sample container, anda curve showing a relation between a temperature change and acalorimetric change is referred to as DTA curve.

It is generally known that, when an exothermal reaction occurs, apositive peak appears on the DTA curve. Furthermore, thethermogravimetry/differential thermal analysis (generally referred to asTG/DTA) is known as a method for simultaneously executing thethermogravimetry and the differential thermogravimetric analysis. Inthis TG/DTA, it is possible to simultaneously monitor a change in aweight of a sample and an endothermal or exothermal reaction when asample is heated, and therefore the technique can be applied to accesscompositions or thermal properties of various substances.

The hollow silica microparticles according to the present invention showexcellent effects not provided by conventional silica microparticles orhollow silica microparticles. More specifically, because of theexcellent effects, for instance, when a composition for forming atransparent coating film prepared by mixing the hollow silicamicroparticles according the present invention with a binder is cured ona substrate, a transparent film-coated substance having excellentproperties can be obtained. Different from a transparent film-coatedsubstrate prepared by using the composition for forming a transparentcoating film containing known silica microparticles or hollow silicamicroparticles, with the hollow silica microparticles according to thepresent invention, it is possible to provide a transparent film-coatedsubstrate capable of suppressing whitening and having improved abrasionresistance and adhesiveness.

Namely, in the transparent film-coated substrate containing the hollowsilica microparticles according to the present invention which have thecalorimetric and thermogravimetric properties as described above,whitening can be suppressed and the abrasion resistance and theadhesiveness are improved. On the other hand, in transparent film-coatedsubstrates containing the conventional type of hollow silicamicroparticles, hollow silica microparticles not having been subjectedto surface processing with a silane compound, hollow silicamicroparticles not remarkable weight loss at a temperature in the rangefrom 200° C. to 500° C., or those having been subjected to surfaceprocess different from that employed in the method of producing hollowsilica microparticles according to the present invention, whiteningoccurs in the transparent coating films, and the abrasion resistance andthe adhesiveness are not sufficient.

In contrast, in the hollow silica microparticles according to thepresent invention, the organosilyl groups present on a surface of thehollow silica microparticles directly bond to silicon atoms respectivelywith the structure of —Si—O—SiR₃ (R: an organic group) also present on asurface of the particles in the stable state at a temperature of up to200° C., which is guessed as a reason for suppression of aggregation ofsilica microparticles in the transparent coating film causing whiteningin the transparent coating film because the organosilyl groups arepresent therein as substitutional groups tightly bonded to surfaces ofthe hollow silica microparticles when a transparent film-coatedsubstrate is formed. Furthermore, it can be considered that presence ofthe organosilyl group contributes to improvement in dispersibility ofsilica microparticles in an organosol and a transparent coating film aswell as to making more fine-grained the transparent coating film becauseof a chemical bond with a binder resin, and that the properties giveexcellent abrasion resistance and adhesiveness to the transparentcoating film.

On the other hand, in a case of the conventional hollow silicamicroparticles, an organosilyl group is not present on a surfacethereof, so that the effects observed when the hollow silicamicroparticles according to the present invention are used is notprovided by the conventional hollow silica microparticles. Furthermore,in a case of hollow silica microparticles not subjected to surfaceprocessing by the method employed when the hollow silica microparticlesaccording to the present invention are produced, weight loss of 1.0 W %or more due to heat can not be observed at a temperature of 200° C. ormore, and therefore it can be considered that a strong bond is notformed when the particles are subjected to surface processing, and itmay be said that the effects as provided by the hollow silicamicroparticles according to the present invention are hardly achievedalso in this case like in a case of the conventional hollow silicamicroparticles.

In the case of the hollow silica microparticles according to the presentinvention, in addition to the thermogravimetric properties as describedabove, a specific peak is observed at a temperature in the range from200° C. to 500° C. also in differential thermogravimetric analysis,while the peak is not observed in the cases of conventional hollowsilica microparticles and hollow silica microparticles not subjected tosurface processing in the same way as that employed in the method ofproducing hollow silica microparticles according to the presentinvention.

It is known that a peak in the DTA curve indicates occurrence of anexothermal reaction associated with separation of an organic group. Inthe present invention, generally a peak in the DTA curve appears at atemperature range (from 200° C. to 500° C.) where the thermogravimetricproperty described above appear.

An average particle diameter of the hollow silica microparticlesaccording to the present invention is preferably in the range from 5 to300 nm. The hollow silica microparticles having the average particlediameter in this range are preferable for obtaining a transparentcoating film. It is difficult to obtain hollow silica microparticleswith the average particle diameter of less than 5 nm. When the averageparticle diameter is more than 300 nm, scattering of light becomesremarkable, and when the hollow silica microparticles are processed intoa thin film, the reflection is high, which spoils the antireflectioncapability. The average diameter of the hollow silica microparticlesaccording to the present invention is more preferably in the range 10 to200 nm, and further more preferably in the range from 10 to 100 nm.

A specific surface area of the hollow silica microparticles according tothe present invention is preferably in the range from 50 to 1500 m²/gfor obtaining dispersibility and stability of the hollow silicamicroparticles in a solvent or at the step of processing the hollowsilica microparticles into a film. When the specific surface area isless than 50 m²/g, it is difficult to obtain hollow silicamicroparticles having a low refractive index. On the other hand, whenthe specific surface area is over 1500 m²/g, the dispersibility andstability of the hollow silica microparticles become lower, which is notdesirable. The specific surface area of the hollow silica microparticlesaccording the present invention is preferably in the range from 50 to200 m²/g.

The hollow silica microparticles according to the present invention arerequired to show weight loss of 1.0 W % or more in thermogravimetry at atemperature in the range from 200° C. to 500° C. In a transparentfilm-coated substrate in which the hollow silica microparticles showingweight loss due to heat of less than 1.0 W % are blended therein,whitening occurs, and both the abrasion resistance and the adhesivenessare insufficient. A degree of the weight loss due to heat is preferably1.05 W % or more, and more preferably 1.5 W % or more at a temperaturein the range from 200 to 500° C.

The hollow silica microparticles according to the present inventionpreferably show a peak when measured by the differentialthermogravimetric analysis at a temperature in the range from 200° C. to500° C. Generally, when the hollow silica microparticles show the weightloss due to heat in the same temperature range, at least one peak can beobserved in the differential thermogravimetric analysis.

The hollow silica microparticles according to the present invention havean organic group directly bonded to a silicon atom on a surface thereof.There is not specific restriction concerning a type of the organicgroup, and any type of organic group is allowable on the condition thatthe organic group has affinity with a binder used when a composition forforming a transparent coating film is prepared, especially with anorganic resin, does not cause whitening of a transparent coating film ina transparent film-coated substrate obtained by curing the compositionfor forming a transparent coating film on a substrate, nor spoils theabrasion resistance and the adhesiveness. For instance, the organicgroup may be a hydrocarbon group or that having an atom other than acarbon atom and a hydrogen atom. The hydrocarbon group may be eitheraliphatic or aromatic, and also may be a saturated hydrocarbon group oran unsaturated one. The organic group may have a double bond or a triplebond, and also may have an ether bond.

The atoms other than a carbon atom and a hydrogen atom include, but notlimited to an oxygen atom, a nitrogen atom, a fluorine atom, a chlorineatom, a bromide atom, a sulfur atom, a silicon atom, a boron atom, analuminum atom, a magnesium atom, a sodium atom, a lithium atom, acalcium atom, and a potassium atom.

A preferable example of the organic group directly bonding to a siliconatom is, for instance, one selected from the group consisting ofsaturated or unsaturated hydrocarbon groups having 1 to 18 carbon atomsand halogenated hydrocarbon groups having 1 to 18 carbon atoms. Morespecifically, the preferable organic groups include, but not limited toa 3-methacryloxy propyl group, a 3-acryloxy propyl group,3,3,3-trifluoropropyl group, a methyl group, a phenyl group, an isobutylgroup, a vinyl group, a γ-glycidoxy tripropyl group, a γ-methacryloxypropyl group, an N-β (aminoethyl) γ-aminopropyl group, anN-β(aminoethyl) γ-aminopropyl group, a γ-aminopropyl group, and anN-phenyl-γ-aminopropyl group.

The hollow silica microparticles according to the present invention aregenerally dispersed in an organic solvent. A concentration of silica ispreferable in the range from 1 to 70 W % from the viewpoint ofstability, and more preferably in the range from 3 to 40 W %.

Preferable Example of the Hollow Silica Microparticles (1)

From the view points of the adhesiveness of a transparent coating filmcontaining the hollow silica microparticles according to the presentinvention, capability to suppress whitening of a coating film, and theabrasion resistance, the hollow silica microparticles according to thepresent invention preferably have the organic group expressed by generalformula (1) or general formula (2) below, and also preferably showweight loss of 1.5 W % or more when measured by the thermogravimetry(TG) at a temperature in the range from 200° C. to 500° C.:

—R—OC(═O)CCH₃═CH₂  General formula (1):

(R: A bivalent hydrocarbon group having 1 to 12 carbon atoms)

—R—OC(═O)CH═CH₂  General formula (2):

(R: A bivalent hydrocarbon group having 1 to 12 carbon atoms)

Preferable Example of the Hollow Silica Microparticles (2)

Also for the similar reasons, the hollow silica microparticles accordingto the present invention preferably have the organic group expressed bythe following general formula (3):

—R—C_(n)F_(a)H_(b)  General formula (3):

(a+b=2n+1, n is an integer of 1 to 3, while R is a bivalent hydrocarbongroup having 1 to 12 carbon atoms).

Preferable Example of the Hollow Silica Microparticles (3)

From the view points not only of the adhesiveness of a transparentcoating film containing the hollow silica microparticles according tothe present invention, capability to suppress whitening of a coatingfilm, and the abrasion resistance, but also of the effect to have thehollow silica microparticles unevenly distributed in the transparentcoating film in the layered state as described above, preferably thehollow silica microparticles according to the present invention have anaverage particle diameter of 5 to 300 nm when measured by the dynamiclight scattering method, and a specific surface area of 50 to 1500 m²/g,and also have an outer shell in which cavities are formed therein.Furthermore, the hollow silica microparticles according to the presentinvention preferably show weight loss of 1.0 W % or more at atemperature in the range from 200° C. to 500° C. and also show apositive DTA peak when measured by the differential thermogravimetricanalysis in the same temperature range and have an organic groupdirectly bonding to a silicon atom on a surface thereof. The hollowsilica microparticles according to the present invention especiallypreferably have the surface charge (Q_(A)) in the range from 5 to 20μeq/g.

[Method of Producing the Hollow Silica Microparticles]

The hollow silica microparticles according to the present invention areproduced by using any known hollow silica microparticles as a rawmaterial. Generally, the hollow silica microparticles have fine pores inthe outer shell. In the hollow silica microparticles according to thepresent invention, the outer shell may have fine pores, but the finepores may disappear due to heating while being produced by theproduction method as described below.

The hollow silica microparticles used as a raw material in the presentinvention should have the average particle diameter of 5 to 300 nm andthe specific surface area of 50 to 1500 m²/g.

The hollow silica microparticles, which are used as a raw material inthe present invention, are produced by simultaneously adding an aqueoussolution of a silicate and/or an acidic silicic acid solution and anaqueous solution of an alkali-soluble inorganic compound to an alkaliaqueous solution with the pH of 10 or more, or to an alkali aqueoussolution with the pH of 10 or more in which seed particles aredispersed, if required, to prepare a dispersion liquid of core particleswith the molar ratio of silica versus the inorganic compounds other thansilica in the range from 0.3 to 1.0; adding a silica source to thedispersion liquid to form a first silica coating layer on the coreparticles; and then adding an acid to the dispersion liquid to remove aportion or all of the elements constituting the core particles (Refer toPatent document 6). Furthermore, an alkali aqueous solution, an organicsilicon compound and/or a partial hydrolyte thereof are added to thedispersion liquid of the hollow silica microparticles as described aboveto form a second silica coating layer on the microparticles (Also referto Patent document 6).

In the method of producing hollow silica microparticles according to thepresent invention, at first an organosol of the hollow silicamicroparticles is prepared, and a concentration of silica as a solidcomponent is in the range from 1 to 70 W %.

For instance, a silica sol containing hollow silica microparticlesprepared by using water as a dispersant is subjected to solventsubstitution to obtain an organosol to be used in the present invention.Generally a ultrafilter membrane or a rotary evaporator is used toobtain an organosol with a concentration of silica as a solid componentin the range from 1 to 70 W %.

An organic solvent is used in solvent substitution for the silica solcontaining hollow silica microparticles prepared by using water as adispersant. There is no specific restriction over the type of organicsolvent so long as the solvent does not give any negative influence tocoating a surface of the hollow silica microparticles with a silanecompound. Examples of the organic solvent include, for instance,alcohols, glycols, esters, ketones, nitrogen compounds, and aromatichydrocarbons. Generally alcohols such as methanol and ethanol areselected.

A concentration of silica as a solid component varies to solvents, andwhen the concentration is 70 W % or more, the hollow silicamicroparticles are hardly dispersed in the solvent, and theconcentration of less than 1 W % is not practical.

In the production method according to the present invention, anorganosol with a silica concentration of 1 to 70 W % is prepared, and asilane compound and an alkali catalyst are added to the organosol at atemperature in the range from 30° C. to 300° C. to react the silanecompound to the hollow silica microparticles under the condition that aquantity of water against a quantity of added silica is in the rangefrom 0.1 to 50 W %.

A quantity of added silane compound is generally in the range from 1 to50 weight portions against 100 weight portions of the hollow silicamicroparticles. When the quantity is less than 1 weight portions, apercentage of the hollow silica microparticles not processed becomes toohigh, which is not preferable. On the other hand, when the percentage isover 50 weight portions, a quantity of the silane compound is excessiveand not economical. A quantity of added silane compound is preferably inthe range from 3 to 25 weight portions.

The silane compound used in the production method according to thepresent invention is generally expressed with the chemical expression ofR_(n)SiX_((4-n)) (R: an organic group, X; a hydrolyzable group, and n:an integer of 0 to 3). More specifically, the silane compounds include,but not limited to tetramethoxysilane, tetraethoxysilane,tetraisopropoxysilane, methyl trimethoxysilane, dimethyldimethoxysilane, phenyl trimethoxysilane, diphenyl dimethoxysilane,methyl triethoxysilane, dimethyl diethoxysilane, phenyl triethoxysilane,diphenyl diethoxysilane, isobutyl trimethoxysilane, vinyltrimethoxysilane, vinyl triethoxysilane, vinyl-tris-(β-methoxyethoxy)silane, 3,3,3-trifluoropropyl trimethoxysilane,methyl-3,3,3-trifluoropropyl dimethoxysilane, β-(3,4 epoxy cyclohexyl)ethyl trimethoxysilane, γ-glycidoxytripropyl trimethoxysilane,γ-glycidoxypropyl methyl diethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropyl methyl dimethoxysilane,γ-methacryloxypropyl trimethoxysilane, γ-methacryloxypropyl methydiethoxysilane, γ-methacryloxypropyl triethoxysilane, N-β(aminoethyl)γ-aminopropyl methyl dimethoxysilane, N-β(aminoethyl) γ-aminopropyltrimethoxysilane, N-β(aminoethyl) γ-aminopropyl triethoxysilane,γ-aminopropyl trimethoxysilane, γ-aminopropyl triethoxysilane,N-phenyl-γ-aminopropyl trimethoxysilane, γ-mercaptopropyltrimethoxysilane trimethyl silanole, methyl trichlorosilane, methyldichlorosilane, dimethyl dichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyl dichlorosilane, vinyl trichlorosilane,trimethyl bromosilane, diethylsilane, and acryloxypropyl methoxysilane.

Of these substances, silane having an acrylic group, silane having amethacrylic group, and the 3,3,3-trifluoropropyl trimethoxysilane areespecially preferable.

There is no specific restriction over a quantity of added alkalicatalyst, and although the quantity varies according to a type of thealkali catalyst, the quantity of added alkali is preferably in the rangefrom 20 to 2,000 ppm against a quantity of the organosol in which thehollow silica microparticles are dispersed. When the quantity is lessthan 20 ppm, sometimes the reaction of the silane compound on thesurface of the hollow silica does not proceed. On the other hand, whenthe quantity is over 2,000 ppm, sometimes dispersibility of the hollowsilica microparticles in a binder may drop because of the surplusalkali, or other negative influences may occur due to the alkalicatalyst remaining in the composition for forming a transparent coatingfilm.

There is no specific restriction over a type of the alkali catalyst usedin the present invention, and such catalysts as an ammonia, a hydroxideof an alkali metal, or an amine compound are advantageously used. Thealkali catalyst may be added as an aqueous solution thereof.

A quantity of water in a reactant solution is preferably in the rangefrom 0.1 to 50 W %, more preferably 10 W % or below, and still furtherpreferably 5 W % or below against a quantity of added silica (the hollowsilica microparticles). When the quantity of water is in the range from0.1 to 50 W %, a surface of the hollow silica microparticles reacts withthe silane compound and the surface processing is carried outefficiently. When the quantity is less than 0.1 W %, the efficiency ofthe surface processing is low, and the processing is not carried out inthe stable state. When the quantity is 50 W % or more, the silanecompounds are apt to react with themselves, and as a result the surfaceprocessing of the hollow silica microparticles is not carried outsufficiently.

When a reaction between the hollow silica microparticles and the silanecompound is performed at a temperature of less than 30° C., the reactionspeed is low, so that employment of a reaction temperature of less than30° C. is not practical. On the other hand, when the reactiontemperature is over a boiling point of the organosol solvent, thesolvent evaporates to cause increase of the water content, which is notpreferable. When the reaction is carried out by using a pressurecontainer, the reaction may be carried out at a temperature of up to300° C. Preferably the reaction temperature should be 40° C. or more butless than a boiling point of the solvent.

When a period of time for the reaction between the hollow silicamicroparticles and the silane compound is less than 0.1 hours, sometimesthe reaction does not proceed sufficiently, and therefore employment ofthe reaction time of less than 0.1 hours is not practical. On the otherhand, when the reaction time is over 100 hours, such parameters as theyield are not improved, so that it is not necessary to make the reactionproceed for so long a time. Preferably the reaction time is set to therange from 3 hours to 30 hours.

There is no specific restriction over the sequence of adding the silanecompound and the alkali catalyst to the organosol in which the hollowsilica microparticles are dispersed, and it is allowable (1) to add thealkali catalyst first and then add the silane compound, (2) to add thesilane compound first and then add the alkali catalyst, or (3) tosimultaneously add the silane compound and the alkali catalyst, but thesequence (1) or (2) is relatively preferable.

Example of a Method of Producing Hollow Silica Microparticles (1)

The present invention provides a method of hollow silica microparticles,the method comprising the steps of preparing an organosol with thesilica concentration of 1 to 70 W % in which the hollow silicamicroparticles according to the present invention are dispersed in anorganic solvent; and adding a silane compound and an alkali catalyst tothe organosol to react the silane compound with the hollow silicamicroparticles under the condition that a quantity of water is in therange from 0.1 to 50 W % against a quantity of silica blended therein ata temperature in the range from 30 to 300° C. Preferably the quantity ofadded silane compound is in the range from 1 to 50 weight portionsagainst 100 weight portions of the hollow silica microparticles, whilethe concentration of added alkali catalyst in the organosol ispreferably in the range from 20 to 2,000 ppm.

The hollow silica microparticles obtained by the production methodaccording to the present invention show weight loss of 1.0 W % or morewhen measured by the thermogravimetry (TG) at a temperature in the rangefrom 200° C. to 500° C., and also show a positive DTA peak when measuredby the differential thermogravimetric analysis (DTA) in the sametemperature range, and the composition for forming a transparent filmcontaining the hollow silica microparticles and the binder as describedabove is excellent in the adhesiveness with a substrate, the capabilityof preventing whitening, and abrasion resistance.

Example of a Method of Producing Hollow Silica Microparticles (2)

The present invention provides in another aspect a different method ofproducing hollow silica microparticles, and the method comprises thesteps of producing an organosol with the silica concentration of 1 to 70W % in which hollow silica microparticles are dispersed, and adding asilane compound and/or a multifunctional acrylic acid ester resin havinga hydrophobic functional group, and an alkali catalyst to the organosolat a temperature in the range from 30° C. to 300° C. to react the silanecompound to the hollow silica microparticles under the condition where aquantity of water against a quantity of added silica is in the rangefrom 0.1 to 50 W %.

In the production method in this aspect of the present invention, amultifunctional acrylic acid ester resin having a hydrophobic functionalgroup, or a mixture of a silane compound and the multifunctional acrylicacid ester resin having a hydrophobic functional group is used in placeof the silane compound used in the production method described above.

The multifunctional acrylic acid ester resins having a hydrophobicfunctional group in the production method include, but not limited topentaerythrytol triacrylate, pentaerythrytol tetraacrylate, trimethylolpropane tri(metha)acrylate, pentaerythrytol tetraacrylate,ditrimethylolpropane tetra(metha)acrylate, dipentaerythrytolhexaacrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, isodecylmethacrylate, n-lauryl acrylate, n-stearyl acrylate, 1,6-hexanedioldimethacrylate, perfluorooctylethyl methacrylate, trifluoroethylmethacrylate, urethane acrylate.

When the multifunctional acrylic acid ester resin having hydrophobicityis used, there is not any specific restriction over the weight ratio ofthe resin versus the hollow silica microparticles (a weight of themultifunctional acrylic acid ester resin having hydrophobicity versus aweight of the hollow silica microparticles), but generally the ratio of0.001 to 2 is preferable, and the ratio of 0.005 to 1.5 is furtherpreferable.

[Compositions for Forming a Transparent Coating Film]

The composition for forming a transparent coating film contains thehollow silica microparticles according to the present invention and abinder.

The binder is a component enabling formation of a coating film on asurface of a substrate, and is selected from such materials as organicresins from the view points of adhesiveness to a substrate, hardness,adaptability to coating, and the like. An organic resin, a hydrolysableorganic silicon compound, or a partial hydrolyte thereof is selectedaccording to the necessity, and the component is generally dispersed ina solvent for use.

Examples of the binder include, but not limited to a polyester resin, anacrylic resin, a urethane resin, a vinyl chloride resin, an epoxy resin,a melamine resin, a fluorine resin, a silicone resin, a butyral resin, aphenol resin, a vinyl acetate resin, a UV cure resin, an electron beamcure resin, an emulsion resin, a water-soluble resin, a hydrophilicresin, a mixture of the resins, a resin for coating such as a copolymerof the resins or a denatured one, a hydrolysable organic siliconcompound such as alcoxysilane, or partial hydrolytes thereof. When ahydrolysable organic silicon compound is used as a binder, for instance,water and a catalyst (an acid or an alkali) are added to a mixturesolution of alkoxysilane and alcohol to prepare a partial hydrolyte ofthe alkoxysilane, and the partial hydrolyte is used as the binder.

The composition for forming a transparent coating film according to thepresent invention contains 10 to 10,000 weight portions of the binder asa solid phase against 100 weight portions of silica in the hollow silicamicroparticles (silica contained therein). When the quantity of thebinder is less than 10 weight portions, sometimes a desired hardness ofthe coating film can not be obtained, or the composition is not cured.When the quantity is over 10,000 weight portions, the desired lowrefractive index is not provided. A quantity of the added binder against100 weight portions of the hollow silica microparticles is preferably inthe range from 50 to 1000 weight portions.

The composition for forming a transparent coating film according to thepresent invention may contain a photoinitiator, a catalyst for curing,or the like according to a method of curing the binder.

Examples of the photoinitiator and catalysts for curing include, but notlimited to radical initiators such as peroxides, and azo compounds,titanium compounds, tin compounds, platinum catalyst, and isocyanate.

The composition for forming a transparent coating film according to thepresent invention is generally prepared by mixing an organosol in whichthe hollow silica microparticles according to the present invention aredispersed with a binder. The binder may be dispersed with an organicsolvent as described above. Mixing of the organosol and the binder maybe performed in the range of the weight ration described above by usinga mixer or the like with active agitation to obtain the composition forforming a transparent coating film according to the present invention.

The composition for forming a transparent coating film according to thepresent invention contains an organic solvent originated from theorganosol or the binder, and is diluted with an organic solventaccording to the application. In this case, the composition for forminga transparent coating film according to the present invention ispreferably diluted with 100 to 5000 weight portions of an organicsolvent against 100 weight portions of solid components including thehollow silica microparticles according to the present invention and thebinder.

The solvent may be subjected to solvent substitution according to a typeof a surface functional group present on a surface of a used substrateor on a surface of the surface-coated hollow silica microparticles. Thesolvents available for the purpose described above include, but notlimited to alcohols such as methanol, ethanol, isopropanol, n-butanol,and methyl isocarbinol; ketones such as acetone, 2-butanone, ethyl amylketone, diacetone alcohol, isohoron, and cyclohexanone; amides such asN,N-dimethyl formamide, and N,N-dimethyl acetoamide; ethers such asdiethyl ether, isopropyl ether, tetrahydrofuran, 1,4-dioxane,3,4-dihydro-2H-pyran; glycol ethers such as 2-methoxy ethanol, 2-ethoxyethanol, 2-butoxy ethanol, and ethylene glycol dimethyl ether; glycolether acetates such as 2-methoxy ethyl acetate, 2-ethoxy ethyl acetate,and 2-butoxy ethyl acetate; esters such as methyl acetate, ethylacetate, isobutyl acetate, amyl acetate, ethyl lactate, and ethylenecarbonate; aromatic hydrocarbons such as benzene, toluene, and xylene;aliphatic hydrocarbons such as hexane, heptane, iso-octane, andcyclohexane; halogenated hydrocarbons such as methylene chloride,1,2-dichlor ethane, dichloropropane, and chlorbenzene; sulfoxides suchas dimethyl sulfoxide; and pyrrolidones such as N-methy-2-pyrrolidone,and N-octyl-2-pyrrolidone. The dispersing medium may be used singly orin combination. Of these solvents, a polar solvent is especiallypreferable.

It is allowable to add an antiseptic agent, an antibiotic agent, anantifoaming agent, a ultraviolet degradation inhibiting agent, acoloring agent, a leveling agent or the like to the composition forforming a transparent coating film according to the present invention,if required.

Preferable Example of the Composition for Forming a Transparent CoatingFilm (1)

A preferable example of the composition for forming a transparentcoating film according to the present invention contains the hollowsilica microparticles having the surface charge (Q_(A)) in the rangefrom 5 to 20 μeq/g, the binder, and a polar solvent. A concentration(C_(PA)) of the hollow silica microparticles in the preferable exampleis in the range from 0.1 to 20 W %, and a concentration (C_(M)) of thebinder as a solid component is in the range from 1 to 50 W %.

The surface charge (Q_(A)) of the hollow silica microparticles ispreferably in the range from 5 to 20 μeq/g, and more preferably in therange from 6 to 18 μeq/g. When the surface charge (Q_(A)) of the hollowsilica microparticles is in the range described above, the phenomenonthat the hollow silica microparticles are unevenly distributed easilyoccurs in a substrate with a coating film obtained by curing thecomposition for forming a transparent coating film containing the hollowsilica microparticles as described above on a substrate, and the hollowsilica microparticles are unevenly distributed and dispersed in theouter side from a middle point of the coating film in the thicknessdirection. The hollow silica microparticles may be dispersed either inthe single-layered state or in the multi-layered state, and also thehollow silica microparticles may be dotted.

When the surface charge (Q_(A)) of the hollow silica microparticles isless than 5 μeq/g, in the coating film obtained by curing thecomposition for forming a transparent coating film containing the hollowsilica microparticles, the tendency for homogeneous dispersion of thehollow silica microparticles becomes stronger. When the surface charge(Q_(A)) of the hollow silica microparticles is over 20 μeq/g, sometimesthe particles may not be hollow. Furthermore whitening easily occurs inthe coating film obtained by curing the composition for forming atransparent coating film containing the hollow silica microparticles,and the hollow silica microparticles are apt to be dispersedhomogeneously in the coating film.

As for a quantity of hollow silica microparticles contained in thecomposition for forming a transparent coating film, the concentration(C_(PA)) of the hollow silica microparticles is preferably in the rangefrom 0.1 to 20 W %, and a concentration (C_(M)) of the binder as a solidcontent is preferably in the range from 1 to 50 W %.

When the concentration (C_(PA)) of the hollow silica microparticles isless than 0.1 W %, in the coating film prepared by curing thecomposition for forming a transparent coating film containing the hollowsilica microparticles, it is difficult to achieve the opticalcharacteristics and the electric characteristics provided by unevendistribution and dispersion of the hollow silica microparticles. Whenthe concentration (C_(PA)) of the hollow silica microparticles is over20 W %, the tendency for homogeneous dispersion of the hollow silicamicroparticles becomes stronger in the coating film obtained by curingthe composition for forming a transparent coating film containing thehollow silica microparticles. The concentration (C_(PA)) of the hollowsilica microparticles is preferably in the range from 1 to 10 W %.

An average particle diameter of the hollow silica microparticles used inthe present invention is preferably in the range from 5 to 300 nm. Thehollow silica microparticles according to the present invention shouldmore preferably have the average particle diameter in the range from 10to 200 nm, and further preferably in the range from 10 to 100 nm.

The method of producing the composition for forming a transparentcoating film described above is applied also to produce the compositionfor forming a transparent coating film in the preferable example (1) ofthe composition for forming a transparent coating film.

Preferable Example of a Composition for Forming a Transparent CoatingFilm (2)

As another preferable example of the composition for forming atransparent coating film according to the present invention, there canbe enlisted a composition for forming a transparent coating filmcontaining hollow silica microparticles with the surface charge (Q_(A))in the range from 5 to 20 μeq/g, metal oxide particles with the surfacecharge (Q_(B)) in the range from 51 to 150 μeq/g, a binder, and a polarsolvent, and the composition is characterized in that a value of thedifference between the surface charge (Q_(B)) of the metal oxideparticles and the surface charge (Q_(A)) of the hollow silicamicroparticles [(Q_(B))−(Q_(A))] is in the range from 20 to 100 μeq/g,the concentration (C_(PA)) of the hollow silica microparticles is in therange from 0.1 to 20 W %, the concentration (C_(PB)) of the metal oxideparticles is in the range from 0.1 to 20 W %, and the concentration(C_(M)) of the binder as a solid component is in the range from 1 to 50W %.

Because the surface charge (Q_(A)) of the hollow silica microparticlesis in the range from 5 to 20 μeq/g, the surface charge (Q_(B)) of themetal oxide particles is in the range from 51 to 150 μeq/g, and a valueof the difference between the surface charge (Q_(B)) of the metal oxideparticles and the surface charge (Q_(A)) of the hollow silicamicroparticles [(Q_(B))−(Q_(A))] is in the range from 20 to 100 μeq/g,when the composition for forming a transparent coating film is cured andconverted to a coating film, the tendency becomes stronger that themetal oxide particles are unevenly distributed and dispersed in theinner side from the middle point of the transparent coating film in thethickness direction, namely in the side closer to the substrate and thehollow silica microparticles are unevenly distributed and dispersed inthe outer side from the middle point of the coating film in thethickness direction, namely in the side closer to the surface.

It can be guessed that the phenomenon occurs because of the electricalrepulsion between the hollow silica microparticles and the metal oxideparticles. When the value of the difference between the surface charge(Q_(B)) of the metal oxide particles and the surface charge (Q_(A)) ofthe hollow silica microparticles [(Q_(B))−(Q_(A))] is less than 20μeq/g, because the electrical repulsion between the hollow silicamicroparticles and the metal oxide particles is small, the tendencybecomes weaker that the two types of microparticles repulse each otherand are distributed in different portions of the coating film.

When the value of [(Q_(B))−(Q_(A))] is over 100 μeq/g, a difference insurface charge between the two types of microparticles is too large, andthe hollow silica microparticles and the metal oxide particles easilyaggregate respectively.

Both the concentration (C_(PA)) of the hollow silica microparticles andthe concentration (C_(PB)) of the metal oxide particles are preferablyin the range from 0.1 to 20 W % respectively. When the concentrationsare in this range, the hollow silica microparticles and the metal oxideparticles are unevenly distributed and dispersed in the coating filmrespectively. On the other hand, when the concentrations are lower thanthe range, the effects provided by uneven distribution and dispersion ofthe two types of microparticles are hardly shown. When the twoconcentrations are over the range, the tendency becomes stronger thanthe two types of microparticles are distributed and dispersedhomogenously in the coating film. Both of the concentration (C_(PA)) ofthe hollow silica microparticles and the concentration (C_(PB)) of themetal oxide particles are preferably in the range from 1 to 10 W %respectively.

As for the types of the metal oxide particles, if the coating film isused as a hard coat film, metal oxide microparticles of ZrO₂, TiO₂,Sb₂O₅, ZnO₂, Al₂O₃, SnO₂, chained particles in which the microparticlesabove are coupled to each other in the chain-like state, or silicaparticles with the refractive index of 1.45 or below can advantageouslybe used.

When the transparent coating film is used as a high refractive indexfilm, it is preferable to use the metal oxide particles having arefractive index of 1.60 or more, or further preferable to use the metaloxide particles having the refractive index of 1.80 or more, and morespecifically any of ZrO₂, TiO₂, Sb₂O₅, ZnO₂, Al₂O₃, SnO₂, antimony-dopedtin oxide, tin-doped indium oxide, tin oxide-doped phosphorus (PTO) orthe like can advantageously be used.

When the transparent coating film is used as a conductive film, it isgenerally preferable to use, as the metal oxide particles,microparticles of Sb₂O₅, SnO₂, antimony-dopes tin oxide, tin-dopesindium oxide, tin oxide-doped phosphorus (PTO), silica-basedmicroparticles or silica-based microparticles having cavities thereinwith the surface coated with any of the conductive materials.

If required, the metal oxide particles having been processed with thesilane compound may be used, and furthermore, in the method of producinghollow silica microparticles in the fifth aspect of the presentinvention, it is allowable to use metal oxide particles in place of thehollow silica microparticles.

When the composition for forming a transparent coating film containingboth hollow silica microparticles and metal oxide particles is used, byapplying the coating film onto a substrate, it is possible to obtain atransparent coating film-coated substrate coated with the transparentcoating film in which the metal oxide particles are unevenly distributedand dispersed in the inner side from the middle point of the coatingfilm, namely in the side closer to the substrate and the hollow silicamicroparticles are unevenly distributed and dispersed in the outer sidefrom the middle point, namely in the side closer to the surface thereof.

Also in the method of producing a composition for forming a transparentcoating film in the preferable example (2) described above, the metaloxide particles may be added during the process of producing thecomposition for forming a transparent coating film.

Transparent Film-Coated Substrate

The transparent film-coated substrate according to the present inventionis prepared by curing the composition for forming a transparent coatingfilm with or without any other coating film on a substrate.

There is not any specific restriction over a type of the substrate solong as the substrate is a solid material enabling formation of acoating film. It is allowable to use, as the substrate, for instance,glass, polycarbonate, acryl resin, PET, TAC (triacetyl cellulose), an MSsubstrate (a copolymer of methyl methacrylate and styrene), apolyolefin-based substrate, or the like. Forms of the substratesinclude, for instance, a plastic sheet, a plastic film, a plastic lens,a plastic panel, a cathode-ray tube, a fluorescent display tube, aliquid crystal display panel, or the like.

As the other examples of coating film, there can be enlisted, forinstance, a hard coat film, a flattened film, a high refractive indexfilm, an insulating film, a conductive resin film, a conductive metalmicroparticle film, a conductive metal oxide microparticle film, a filmmade of a primer or the like.

It is to be noted that the transparent film-coated substrate accordingto the present invention may be further coated for any specificapplication.

The transparent film-coated substrate according to the present inventioncan be obtained by applying the composition for forming a transparentcoating film onto a substrate with any known method such as the dipmethod, the spray method, the spinner method, or the roll coat method,drying the composition, and furthermore curing the applied compositionby heating or by irradiation of ultraviolet rays according to thenecessity.

When the composition is cured by irradiating ultraviolet rays, forinstance, the composition for forming a transparent coating filmaccording to the present invention is applied onto a substrate, then theapplied composition is preliminarily dried at a temperature in the rangefrom 70° C. to 100° C., and then is cured by irradiating ultravioletrays with a high-pressure mercury lamp or a fusion lamp by adjusting thewavelength to an absorption wavelength of the initiating agent, namelyto the range from 300 to 1,000

A refractive index of the transparent coating film according to thepresent invention formed on a substrate varies according to a mixingratio of hollow silica microparticles versus a binder and also accordingto a refractive index of the binder, generally the refractive index islow, namely in the range from 1.15 to 1.42.

Preferable Example of a Transparent Film-Coated Substrate (1)

As a preferable example of the transparent film-coated substrateaccording to the present invention, there can be enlisted, for instance,a transparent film-coated substrate in which the hollow silicamicroparticles having the average particle diameter of 5 to 300 nm and abinder are distributed on a surface thereof (with the film thickness of100 nm to 10000 nm). In this transparent film-coated substrate, thehollow silica microparticles are unevenly distributed and dispersed inthe outer side from a middle point of the coating film, namely in theside closer to the surface.

In the transparent film-coated substrate, the hollow silicamicroparticles are unevenly distributed and dispersed in the outer sidefrom a middle point of the coating film in the thickness direction,namely in the side closer to the surface as described above, and alsothe hollow silica microparticles are present in the single-layered stateor in the multilayered state, or may be dotted. When the hollow silicamicroparticles are unevenly distributed and dispersed in thesingle-layered state or in the multilayered state, the transparentcoating film shows the strong effect of preventing reflection caused bya low refractive index of the hollow silica microparticles or ofpreventing electrification due to conductivity of the hollow silicamicroparticles.

Preferable Example of a Transparent Film-Coated Substrate (2)

Another preferable example of the transparent film-coated substrateaccording to the present invention is a transparent film-coatedsubstrate having a transparent coating film (with the film thickness of100 nm to 10000 nm) which is formed on a surface of the substrate and inwhich metal oxide microparticles with the average particle diameter of 1to 50 nm, the hollow silica microparticles with the average particlediameter of 5 to 300 nm, and a binder are distributed. The transparentfilm-coated substrate is furthermore characterized in that the metaloxide microparticles are unevenly distributed and dispersed in the innerside from a middle point of the transparent coating film, namely in theside closer to the substrate, and the hollow silica microparticles areunevenly distributed and dispersed in the outer side from the middlepoint, namely in the side closer to the surface.

Because the hollow silica microparticles and the metal oxidemicroparticles are present in the single-layered state or in themultilayered state, the transparent film-coated substrate has both thecharacteristics provided by the hollow silica microparticles (includingthe property to prevent reflection and the property to preventelectrification) and the characteristics provided by the metal oxidemicroparticles (including the abrasion resistance, adhesiveness to thesubstrate, properties cause of the high refractive index, conductivity,and the like).

INDUSTRIAL APPLICABILITY

The composition for forming a transparent coating film containing thehollow silica microparticles according to the present invention and thetransparent film-coated substrate according to the present invention canbe applicable to various applications requiring a low refractive index,abrasion resistance, and adhesiveness, and can be used in surfacecoating for display devices, in optical coating for lenses or the like.

Example for Reference Preparation of Hollow Silica Microparticles as aRaw Material

100 g of a silica sol containing silica microparticles with the averagediameter of 5 nm and having the SiO₂ concentration of 20 W % was mixedwith 1900 g of pure water to prepare a mother liquid for reactions, andthe mother liquid was heated to 80° C. pH of the mother liquid was 10.5,and 9,000 g of an aqueous solution of sodium silicate with the SiO₂concentration of 1.17 W % and 9,000 g of sodium aluminate with the Al₂O₃concentration of 0.83 W % were simultaneously added to the motherliquid. During this process, a temperature of the reactant liquid waspreserved at 80° C. pH of the reactant liquid rose to 12.5 immediatelyafter addition of the sodium silicate and sodium aluminate, and thenchanged little. After completion of the materials, the reactant liquidwas cooled down to the room temperature and cleaned with an ultrafiltermembrane to prepare a dispersion liquid of primary particles containingSiO₂ and Al₂O₃ with the solid component concentration of 20 W %.

Then 500 g of the dispersion liquid of primary particles containing SiO₂and Al₂O₃ was sampled, and 1,700 g of pure water was added to thesample. The mixture liquid was heated to 98° C. and 50,400 g of sodiumsulfate with the concentration of 0.5 W % was added to the mixtureliquid preserved at the temperature above. Then, 3,000 g of the sodiumsilicate aqueous solution with the SiO₂ concentration of 1.17 W % and9,000 g of the sodium aluminate aqueous solution with the Al₂O₃concentration of 0.5 W % were added to the mixture liquid to obtain adispersion liquid of composite oxide microparticles. The dispersionliquid was cleaned with a ultrafilter membrane to obtain a dispersionliquid of composite oxide microparticles with the solid phaseconcentration of 13 W %.

1,125 g of pure water was added to 500 g of the dispersion liquid of thecomposite oxide particles, and furthermore concentrated hydrochloricacid (35.5%) was dripped into the mixture liquid to adjust the pH to 1.0for removing aluminum. Then, the dissolved aluminum salt was separatedwith a ultrafilter membrane adding 10 litters of hydrochloric acidaqueous solution with the pH of 3 and 5 litters of pure water andcleaned to obtain a dispersion liquid of silica-based microparticles (1)with the solid phase concentration of 20 W %.

1500 g of the aqueous dispersion liquid of the silica-basedmicroparticles with the solid phase concentration of 20 W %, 500 g ofpure water, 1,750 g of ethanol, and 626 g of 28% ammonia water weremixed, and the mixture liquid was heated to 35° C. Then 104 g of ethylsilicate (with the SiO₂ concentration of 28 W %) was added to the heatedmixture solution to form a silica coating film. Then, the mixturesolution was cleaned with a ultrafilter membrane, adding 5 litters ofpure water, to prepare a dispersion liquid of the silica-basedmicroparticles (2) with the solid phase concentration of 20 W %.

Then, the dispersion liquid of the silica-based microparticles (2) wassubjected to hydrothermal processing for 11 hours at 200° C., and thedispersion liquid was cleaned with a ultrafilter membrane, adding 5litters of pure water, to adjust the solid phase concentration to 20 W%. Then, by using a ultrafilter membrane, a dispersion medium of thedispersion liquid was substituted with ethanol to prepare an organosolwith the solid phase concentration of 20 W %.

The organosol contained hollow silica microparticles with the averageparticle diameter of 46 nm, the specific surface area of 123 m²/g, andthe pore volume of 0.4596 ml/g. This organosol is referred to as “hollowsilica sol A” hereinafter.

Example 1 Preparation of the Hollow Silica Microparticles According tothe Present Invention

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then a 28% ammonia aqueous solution was added to 100 g of the organosolso that the ammonia concentration would be 100 ppm, and the mixturesolution was sufficiently mixed. Then 4 g of methacrylsilane (producedby Shin-Etsu Chemical Co., Ltd.: KBM503) (by about 20 weight portionsagainst 100 weight portions of SiO₂) was added to the mixture solutionto obtain a reactant liquid (with the water content of 0.6 W % againstthe amount of SiO₂). The reactant liquid was heated to 50° C. andpreserved at the temperature for 15 hours with agitation. After theheating process was completed, the reactant liquid was cooled down tothe room temperature and cleaned with a ultrafilter membrane to preparean organosol containing coated hollow microparticles with the SiO₂concentration of 20 W %.

[Analysis of the Hollow Silica Sol Containing Surface-Coated SilicaParticles]

An average particle diameter and a specific surface area of theparticles contained in the organosol were measured. Furthermore thethermogravimetry and differential thermogravimetrical analysis (TG andTDA) were simultaneously conducted for the organosol, and furthermore asurface charge of the microparticles was measured. A result of themeasurement is shown in Table 1 together with results in other examplesand in comparative examples.

Average Particle Diameter

The average particle diameter was measured with a particle diameterdistribution measurement device (produced by Otsuka Electronics Co.,Ltd.: LP-510 Model PAR-III based on the measurement principle of lightscattering method) by the light scattering method using a laser beam.

More specifically, the sample silica sol was diluted with a 0.58%ammonia water to adjust the silica concentration to 1 W %, and theaverage particle diameter was measured with the particle diametermeasurement device described below.

Specific Surface Area

50 ml of sample sol was dried for 20 hours at 110° C., and the specificsurface area was measured with the specific surface area measurementdevice (produced by Yuasa Ionics CO. Ltd.: Multisorb 12) by the nitrogenadsorption method (BET method).

More specifically, HNO₃ was added to 50 ml of the silica sol to adjustthe pH to 3.5, and then 40 ml of 1-propanol was added and the mixturesolution was dried for 20 hours at 110° C. to obtain the sample. Thesample was pulverized in a mortar, and was calcinated for 1 hour at 500°C. in a muffle furnace to obtain a sample for measurement. Then thespecific surface area was calculated with the specific surface areameasurement device (produced by Yuasa Ionics CO. Ltd.: Multisorb 12) bythe nitrogen adsorption method (BET 1-point method).

More specifically, 0.5 g of the sample was put in a measurement cell andwas degassed for 20 minutes at 300° C. in a flow of a mixed gas ofnitrogen by 30 volume % and helium by 70 volume %. Then the sample waspreserved at the liquid nitrogen temperature in the mixed gas flow sothat nitrogen was adsorbed into the sample in the equilibrium state.Then, a temperature of the sample was gradually raised to the roomtemperature by continuously flowing the mixed gas to detect a quantityof nitrogen desorbed in the process, and a specific surface area of thesilica sol was calculated by referred to an analytical curve previouslyprepared.

Concurrent Measurement by Thermogravimetry and DifferentialThermogravimetrical Analysis (TG/DTA)

Concurrent measurement by thermogravimetry and differentialthermogravimetrical analysis was performed with a differentialthermogravimetrical analysis device (produced by Rigaku Corporation:Themoplus TG8110). The measurement was performed in the atmospheric airat the temperature rising rate of 10° C./minute and at a temperaturefrom the room temperature to 500° C.

The sample for the concurrent measurement by thermogravimetry and bydifferential thermogravimetrical analysis (TG/TDA) of the hollow silicamicroparticles employed in Example 1, in all of other examples, and inall of comparative examples was prepared by removing a solvent from theorganosol prepared as described above, sufficiently cleaning theremaining materials to remove hexane, and then drying with areduced-pressure drier. A weight of the powder as the sample was 15 mg,and the sample was used in the measurement.

The hollow silica microparticles used in Examples 1 to 10, Comparativeexample 3, and in Examples 13 to 16 showed a positive peak due to theexothermal reaction at a peak position (temperature) shown in Table 1,when plotting with the X axis indicating a temperature and Y axisindicating a heat value, in the differential thermogravimetric analysis(DTA) performed at a temperature in the range from 200° C. to 500° C.

Surface Charge of Microparticles

As for the method of measuring a surface charge of the hollow silicamicroparticles or the metal oxide microparticles, using the surfacecharge titrimetric measurement device (Mutek Co., pcd-03), a dispersionliquid of the hollow silica microparticles or the metal oxidemicroparticles (with the concentration of 1 W %, 15 g) was titrated with0.001N polychloride diallyl methyl ammonium to obtain a surface charge(μeq/g) per unit grams of the particles. A result is as shown in Table1.

Water contents in the organosol and the reactant liquid (1 ml) weremeasured by putting the samples for measurement in syringesrespectively, and 0.1 g to 0.02 g of the samples were measured with themoisture measuring system (produced by Kyoto Electronic Industries Co.,Ltd., Karl-Fischer moisture measuring system MKC-510). The measurementwas performed in the same way also in other Examples and ComparativeExamples.

Example 2

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then a 28% ammonia aqueous solution was added to 100 g of the organosolso that the ammonia concentration would be 400 ppm, and the mixturesolution was sufficiently mixed. Then 4 g of methacrylsilane (producedby Shin-Etsu Chemical Co., Ltd.: KBM503) (by about 20 weight portionsagainst 100 weight portions of SiO₂) was added to the mixture solutionto obtain a reactant liquid (with the water content of 1.0 W % againstthe amount of SiO₂). The reactant liquid was heated to 50° C. andpreserved at the temperature for 15 hours with agitation. After theheating process was completed, the reactant liquid was cooled down tothe room temperature and cleaned with a ultrafilter membrane to preparean organosol containing coated hollow microparticles with the SiO₂concentration of 20 W %.

Example 3

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then a 28% ammonia aqueous solution was added to 100 g of the organosolso that the ammonia concentration would be 200 ppm, and the mixturesolution was sufficiently mixed. Then 1 g of acrylsilane (produced byShin-Etsu Chemical Co., Ltd.: KBM5103) (by about 5 weight portionsagainst 100 weight portions of SiO₂) was added to the mixture solutionto obtain a reactant liquid (with the water content of 0.75 W % againstthe amount of SiO₂). The reactant liquid was heated to 50° C. andpreserved at the temperature for 15 hours with agitation. After theheating process was completed, the reactant liquid was cooled down tothe room temperature and cleaned with a ultrafilter membrane to preparean organosol containing coated hollow microparticles with the SiO₂concentration of 20 W %.

Example 4

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then a 28% ammonia aqueous solution was added to 100 g of the organosolso that the ammonia concentration would be 200 ppm, and the mixturesolution was sufficiently mixed. Then 2 g of acrylsilane (produced byShin-Etsu Chemical Co., Ltd.: KBM5103) (by about 10 weight portionsagainst 100 weight portions of SiO₂) was added to the mixture solutionto obtain a reactant liquid (with the water content of 0.75 W % againstthe amount of SiO₂). The reactant liquid was heated to 50° C. andpreserved at the temperature for 15 hours with agitation. After theheating process was completed, the reactant liquid was cooled down tothe room temperature and cleaned with a ultrafilter membrane to preparean organosol containing coated hollow microparticles with the SiO₂concentration of 20 W %.

Example 5

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then a 28% ammonia aqueous solution was added to 100 g of the organosolso that the ammonia concentration would be 200 ppm, and the mixturesolution was sufficiently mixed. Then 4 g of acrylsilane (produced byShin-Etsu Chemical Co., Ltd.: KBM5103) (by about 20 weight portionsagainst 100 weight portions of SiO₂) was added to the mixture solutionto obtain a reactant liquid (with the water content of 0.75 W % againstthe amount of SiO₂). The reactant liquid was heated to 50° C. andpreserved at the temperature for 15 hours with agitation. After theheating process was completed, the reactant liquid was cooled down tothe room temperature and cleaned with a ultrafilter membrane to preparean organosol containing coated hollow microparticles with the SiO₂concentration of 20 W %.

Example 6

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then a 28% ammonia aqueous solution was added to 100 g of the organosolso that the ammonia concentration would be 200 ppm, and the mixturesolution was sufficiently mixed. Then 1 g of 3,3,3-trifloropropyltrimethoxysilane (by about 5 weight portions against 100 weight portionsof SiO₂) was added to the mixture solution to obtain a reactant liquid(with the water content of 0.75 W % against the amount of SiO₂). Thereactant liquid was heated to 50° C. and preserved at the temperaturefor 15 hours with agitation. After the heating process was completed,the reactant liquid was cooled down to the room temperature and cleanedwith a ultrafilter membrane to prepare an organosol containing coatedhollow microparticles with the SiO₂ concentration of 20 W %.

Example 7

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then a 28% ammonia aqueous solution was added to 100 g of the organosolso that the ammonia concentration would be 200 ppm, and the mixturesolution was sufficiently mixed. Then 2 g of 3,3,3-trifloropropyltrimethoxysilane (by about 10 weight portions against 100 weightportions of SiO₂) was added to the mixture solution to obtain a reactantliquid (with the water content of 0.75 W % against the amount of SiO₂).The reactant liquid was heated to 50° C. and preserved at thetemperature for 15 hours with agitation. After the heating process wascompleted, the reactant liquid was cooled down to the room temperatureand cleaned with a ultrafilter membrane to prepare an organosolcontaining coated hollow microparticles with the SiO₂ concentration of20 W %.

Example 8

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then a 28% ammonia aqueous solution was added to 100 g of the organosolso that the ammonia concentration would be 200 ppm, and the mixturesolution was sufficiently mixed. Then 4 g of 3,3,3-trifloropropyltrimethoxysilane (by about 20 weight portions against 100 weightportions of SiO₂) was added to the mixture solution to obtain a reactantliquid (with the water content of 0.75 W % against the amount of SiO₂).The reactant liquid was heated to 50° C. and preserved at thetemperature for 15 hours with agitation. After the heating process wascompleted, the reactant liquid was cooled down to the room temperatureand cleaned with a ultrafilter membrane to prepare an organosolcontaining coated hollow microparticles with the SiO₂ concentration of20 W %.

Example 9

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then 4 g of methacrylsilane (produced by Shin-Etsu Chemical Co., Ltd.:KBM503) (by about 20 weight portions against 100 weight portions ofSiO₂) was added to the mixture solution and then the mixture solutionwas sufficiently mixed. Then a 28% ammonia aqueous solution was added to100 g of the organosol so that the ammonia concentration would be 400ppm to obtain a reactant liquid (with the water content of 1.0 W %against the amount of SiO₂). The reactant liquid was heated to 50° C.and preserved at the temperature for 15 hours with agitation. After theheating process was completed, the reactant liquid was cooled down tothe room temperature and cleaned with a ultrafilter membrane to preparean organosol containing coated hollow microparticles with the SiO₂concentration of 20 W %.

Example 10

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith an ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then 4 g of methacrylsilane (produced by Shin-Etsu Chemical Co., Ltd.:KBM503) (by about 20 weight portions against 100 weight portions ofSiO₂) and a 28% ammonia aqueous solution were added simultaneously tothe mixture solution so that the ammonia concentration would be 400 ppmto 100 g of the organosol to obtain a reactant liquid (with the watercontent of 1.0 W % against the amount of SiO₂). The reactant liquid washeated to 50° C. and preserved at the temperature for 15 hours withagitation. After the heating process was completed, the reactant liquidwas cooled down to the room temperature and cleaned with an ultrafiltermembrane to prepare an organosol containing coated hollow microparticleswith the SiO₂ concentration of 20 W %.

Compared Example 1

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith an ultrafilter membrane to prepare 100 g of an organosol with theSiO₂ concentration of 20 W % (and with the water content of 0.5 W %against the amount of SiO₂).

Then 4 g of methacrylsilane (produced by Shin-Etsu Chemical Co., Ltd.:KBM503) (by about 20 weight portions against 100 weight portions ofSiO₂) was added to the mixture solution and then to obtain a reactantliquid (with the water content of 0.5 W % against the amount of SiO₂).The reactant liquid was heated to 50° C. and preserved at thetemperature for 15 hours with agitation. After the heating process wascompleted, the reactant liquid was cooled down to the room temperatureand cleaned with an ultrafilter membrane to prepare an organosolcontaining coated hollow microparticles with the SiO₂ concentration of20 W %.

Comparative Example 2

200 g of the hollow silica sol A (with the solid phase silicaconcentration of 20 W %) was prepared and subjected to solventsubstitution to methanol by using a ultrafilter membrane to obtain 100 gof an organosol with the SiO2 concentration of 20 W % (with the watercontent of 0.5 W % against the amount of SiO₂).

Comparative Example 3

200 g of the hollow silica sol A (with the solid silica concentration of20 W %) was prepared and subjected to solvent substitution to methanolwith a ultrafilter membrane to prepare 100 g of organosol with the SiO₂concentration of 20 W % (with the water content of 0.5 W % againstSiO₂). Then a 28% ammonia aqueous solution was added to 100 g of theorganosol so that the ammonia concentration would be 10 ppm, and themixture solution was sufficiently mixed. Then 4 g of methacrylsilane(produced by Shin-Etsu Chemical Co., Ltd.: KBM503) (by about 20 weightportions against 100 weight portions of SiO₂) was added to the mixturesolution to obtain a reactant liquid (with the water content of 0.5 W %against the amount of SiO₂). The reactant liquid was heated to 50° C.and preserved at the temperature for 15 hours with agitation. After theheating process was completed, the reactant liquid was cooled down tothe room temperature and cleaned with an ultrafilter membrane to preparean organosol containing coated hollow microparticles with the SiO₂concentration of 20 W %.

Example 11 Preparation of a Composition for Forming a TransparentCoating Film

100 g of the organosol obtained in each of Examples 1 to 10 andComparative Examples 1 to 3 (with the solid phase silica content of 20g) and 3 g of a binder (an acrylic resin: Hitaloid 1007 produced byHitachi Chemical Co., Ltd.) were mixed with each other, and aphotoinitiator (1-hydroxy-cyclohexyl-phenyl-ketone, trademark: Irugacure184) was added by 3 W % against a sum of silica and the resin to preparea composition for forming a transparent film.

Example 12 Production of a Transparent Film-Coated Substrate

Each of the compositions for forming a transparent coating film obtainedin Example 11 was applied to a PET film with a bar coater, and was driedfor 1 minute at 80° C. to obtain a transparent film-coated substratewith a transparent coating film having the film thickness of 100 nm.

[Properties and Assessment of a Transparent Film-Coated Substrate]

To assess properties of the transparent film-coated substrate,experiments were conducted to measure the capability to preventwhitening, abrasion resistance, adhesiveness, a refractive index of thetransparent coating film, glare-proof capability, pencil hardness, asurface resistance value, an all-optic transmittance, haze, and areflection coefficient of a ray with the wavelength of 550 nm. The samemeasurement was performed also in Examples 13 to 16 and in ComparativeExample 4 described below. A result is shown in Table 1.

In a case of a PET film not coated with any material, the all-optictransmittance was 90.7%, the hase was 2.0%, and the reflectioncoefficient of the ray with the wavelength of 550 nm was 7.0%.

Adhesiveness

11 parallel flaws were given with a pitch of 1 mm in the horizontal andvertical directions respectively on a surface of a transparentfilm-coated substrate to provide 100 squares, and a cellophane tape(registered trademark) were adhered to the surface of the transparentfilm-coated substrate. Then the cellophane tape was peeled off, and thenumber of squares on which the cellophane tape was not separated andremaining was counted and the count was classified to any of thefollowing 4 grades to assess the adhesiveness.

A: 95 or more

B: 90 to 94

C: 85 to 89

D: 84 or below

Capability to Prevent Whitening

Capability of preventing whitening was measured for each transparentfilm-coated substrate, and a result is shown in Table 1. For assessingthe effect for preventing whitening, a transparent film-coated substratewas put in a drier and was left there for 30 minutes at a temperature of80° C. Presence of cracking or whitening was visually observed, and wasclassified to any of the following three grades.

A: Cracking or whitening was not observed at all.

B: Cracking or whitening was observed a little.

C: Cracking or whitening was observed substantially.

Abrasion Resistance

Abrasion resistance of each transparent film-coated substrate wasmeasured and a result is shown in Table 1. For measuring the abrasionresistance, a piece of #0000 steel wool was used and slid on a surfaceof the substrate 50 times with the load of 500 g/cm². Then a surface ofthe coating film was visually observed and the result was classified toany of the following four grades.

A: No streak flaw was observed.

B: A small number of streak flaws were observed.

C: A large number of streak flaws were observed.

D: The entire surface was scraped off.

Refractive Index of a Transparent Coating Film

A refractive index of each transparent coating film was measured withthe ellipsometer (produced by ULVAC Corp., EMS-1).

Glare-Proof Capability

A black paint was homogeneously sprayed over a rear surface of eachtransparent film-coated substrate and the substrate was placed at aposition 2 meters away from a 30W fluorescent lamp. A perception of thefluorescent lamp was visually checked to assess the glare-proofcapability.

⊚ The fluorescent lamp was not observed at all.

◯ The fluorescent lamp was observed slightly.

Δ The fluorescent lamp was observed, but the contour was blurred.

× The fluorescent lamp was clearly observed.

Pencil Hardness

The pencil hardness was measured according to JIS K 5400 with a pencilhardness tester. Namely, a pencil was set at 45 degrees against asurface of each transparent film-coated substrate, and the pencil wasdrawn at a prespecified speed under a prespecified load to checkpresence of a flaw.

Surface Resistance of Each Transparent Film-Coated Substrate

The surface resistance was measured with a surface resistance meter(produced by Mitsubishi Petrochemical Co., Ltd.: LORESTA).

All-Optic Transmittance and Haze

The all-optic transmittance and the haze were measured with a haze meter(produced by Nippon Denshoku Industries Co., Ltd.: NDH2000).

Reflection Coefficient of a Ray with the Wavelength of 550 nm

The reflection coefficient of a ray with the wavelength of 550 nm wasmeasured with the spectrophotometer (produced by JASCO Corporation:Ubest-55).

TABLE 1 Characteristics of hollow silica microparticles Average particleSpecific Percentage of DTA Peak Surface charge diameter surface areaweight loss position Q_(A)(Q_(B)) nm m²/g % ° C. μeq/g Example 1 47 922.70 280 12.5(−) Example 2 47 75 4.00 280 10.5(−) Example 3 47 103 1.60350 18.8(−) Example 4 47 95 2.50 350 15.5(−) Example 5 47 80 2.50 35012.6(−) Example 6 47 108 1.10 480 11.8(−) Example 7 47 97 1.10 48010.4(−) Example 8 47 83 1.10 480  9.5(−) Example 9 47 78 4.40 28011.1(−) Example 10 47 77 4.50 280   11(−) Comp. Ex 1 26 121 0.41 —28.5(−) Comp. Ex 2 46 121 0.14 — 31.5(−) Comp. Ex 3 47 115 0.65 28026.5(−) Example 13 60 65 4.50 490  8.3(−) Example 14 60 100 3.80 28018.3(−) Example 15 120 99 4.50 350 15.3(−) Example 16 60 65 4.50 490 8.3(52.8) Comp. Ex 4 60 75 0.60 —   25(−) Film performance All- Reflec-Abra- Surface optic tion Prevention sion Refrac- Anti- Pencil Resistransmit- coeffi- of resis- tive glare hard- tance tance Haze cientwhitening tance Adhesion index property ness Ω/□ % % % Ex. 1 A B B 1.30◯ HB 1E14< 93.1 1.0 1.20 Ex. 2 A A B 1.30 ◯ H 1E14< 93.0 1.0 1.30 Ex. 3A A B 1.30 ◯ B 1E14< 93.2 1.0 1.00 Ex. 4 A A B 1.30 ◯ HB 1E14< 93.0 1.01.10 Ex. 5 A A B 1.30 ◯ HB 1E14< 93.1 1.0 1.20 Ex. 6 A A B 1.30 ◯ B1E14< 93.1 1.0 0.90 Ex. 7 A A B 1.30 ◯ HB 1E14< 93.1 1.0 0.80 Ex. 8 A AB 1.30 ◯ H 1E14< 93.2 1.0 0.70 Ex. 9 A A B 1.30 ◯ H 1E14< 93.1 1.0 1.30Ex. 10 A A B 1.30 ◯ H 1E14< 93.0 1.0 1.40 Comp. 1 C C C 1.30 X 3B 1E14<90.4 2.8 1.00 Comp. 2 C C C 1.30 X 3B 1E14< 90.1 2.5 1.00 Comp. 3 B C B1.30 X 3B 1E14< 91.5 1.8 1.20 Ex. 13 A A B 1.30 ◯ 3H 1E14< 93.2 1.0 1.00Ex. 14 A A B 1.30 ◯ 3H 1E14< 93.1 1.0 1.20 Ex. 15 A A B 1.20 ⊚ 3H 1E14<91.4 1.0 0.80 Ex. 16 A A B 1.30 ◯ 3H 3.00E+10 92.8 1.0 0.90 Comp. 4 B CC 1.30 Δ 3B 1E14< 91.9 2.3 1.50

Example 13 Preparation of a Paint (A-1) for Forming a TransparentCoating Film

A component with a low refractive index used in this example was a solin which silica-based hollow microparticles were dispersed (produced byCatalysts and Chemicals Industries Co., Ltd. Thrulya 1420 with theaverage particle diameter of 60 nm, the concentration of 20.5 W %,dispersing medium: isopropanol, refractive index of the particles: 1.30,and a water content of 0.5 W % against an amount of SiO₂), 10 g ofperfluorooctyl ethyl triethoxysilane (produced by Toray Dow CorningCorporation: AY43-158E 100%) was added to 100 g of the sol, and then a28% ammonia aqueous solution was added to the mixture solution so thatthe ammonia concentration would be 400 ppm against 100 g of theorganosol (the water content was 1 W % against the amount of SiO₂). Themixture solution was agitated for 5 hours at 40° C. to obtain a sol inwhich surface-processed hollow microparticles were dispersed (with thesolid phase concentration of 20.3%).

A weight loss of the surface-processed silica-based hollow microparticledispersion sol was measured by the TG-DTA (at a temperature in the rangefrom 200° C. to 500° C.) to find that the weight loss was 4.5%. 0.42 gof an optical initiator (produced by Chibus Specialities (Corp.):Irgacure 184 which is dissolved by IPA and have a solid phaseconcentration of 10%) and 54.08 g of a mixture solution of isopropanoland methyl isobutyl ketone (with the mixing ratio of 1/1) were mixedwith 15.5 g of the surface-processed silica-based hollow microparticledispersion sol and 30 g of hexaerythrythol tripentaacrylate (produced byNippon Kayaku Co., Ltd.: KAYARAD DPHA) to prepare a paint for forming atransparent coating film (A-1).

[Preparation of a Transparent Film-Coated Substrate (1)] (HardCoat+Prevention of Reflection)

The paint for forming a transparent coating film (A-1) was applied on aPET film (with the thickness of 100 μm, the refractive index of 1.65,the substrate transmittance of 88.0%, the haze of 1.0%, and thereflection coefficient of 5.1%) with a bar coater, and the applied paintwas died for 1 minute at 70° C. Then the dried paint was cured byirradiating light from a high pressure mercury lamp (80-W/cm) for 1minute to prepare a transparent film-coated substrate (1). A thicknessof the transparent film-coated substrate was 5 μm. A portion of thetransparent coating film was cut in a direction vertical to thelongitudinal direction, and the cross section was observed with atransmission electron microscope to find that the silica-based hollowmicroparticles form a layer with the thickness of 100 nm in the uppersection, and that only the matrix was present and no particle wasobserved in the lower section.

Example 14 Preparation of a Paint (A-2) for Forming a TransparentCoating Film

A component with a low refractive index used in this example was a solin which silica-based hollow microparticles were dispersed (produced byCatalysts and Chemicals Industries Co., Ltd. Thrulya 1420 with theaverage particle diameter of 60 nm, the concentration of 20.5 W %,dispersing medium: isopropanol, refractive index of the particles: 1.30,and a water content of 0.5 W % against an amount of SiO₂), 1.88 g ofγ-methacrylo oxypropyl trimethoxysilane (produced by Shin-Etsu SiliconeCo., Ltd.: KBM-503 with the SiO₂ content of 81.2%) was added to 100 g ofthe sol, and then a 28% ammonia aqueous solution was added to themixture solution so that the ammonia concentration would be 400 ppmagainst 100 g of the organosol (the water content was 1 W % against theamount of SiO₂). The mixture solution was agitated for 5 hours at 40° C.to obtain a sol in which surface-processed hollow microparticles weredispersed (with the solid phase concentration of 20.3%).

A weight loss of the surface-processed silica-based hollow microparticledispersion sol was measured by the TG-DTA (at a temperature in the rangefrom 200° C. to 500° C.) to find that the weight loss was 3.8%. 0.42 gof an optical initiator (produced by Chibus Specialities (Corp.):Irgacure 184 which is dissolved by IPA and have a solid phaseconcentration of 10%) and 54.08 g of a mixture solution of isopropanoland methyl isobutyl ketone (with the mixing ratio of 1/1) were mixedwith 15.5 g of the surface-processed silica-based hollow microparticledispersion sol, 24 g of pentaerythrythol triacetate (produced byKyoueisha Kagaku Corp.: PE-3A), and 3 g of diethylaminoethylmethacrylate (produced by Kyoueisha Kagaku Corp.: Light ester DE), andthe mixture solution was fully agitated to prepare a paint for forming atransparent coating film (A-2).

[Preparation of a Transparent Film-Coated Substrate (2)] (Prevention ofReflection)

The paint for forming a transparent coating film (A-2) was applied on aPET film (with the thickness of 100 μm, the refractive index of 1.65,the substrate transmittance of 88.0%, the haze of 1.0%, and thereflection coefficient of 5.1%) with a bar coater, and the applied paintwas died for 1 minute at 70° C. Then the dried paint was cured byirradiating light from a high pressure mercury lamp (80-W/cm) for 1minute to prepare a transparent film-coated substrate (2). A thicknessof the transparent film-coated substrate was 5 μm. A portion of thetransparent coating film was cut in a direction vertical to thelongitudinal direction, and the cross section was observed with atransmission electron microscope to find that the silica-based hollowmicroparticles form a layer with the thickness of 100 nm in the uppersection, and that only the matrix was present and no particle wasobserved in the lower section.

Example 15 Preparation of a Paint for Forming a Transparent Coating Film(A-3)

A component with a low refractive index used in this example was a solin which silica-based hollow microparticles were dispersed (produced byCatalysts and Chemicals Industries Co., Ltd. Thrulya 1420-120 with theaverage particle diameter of 120 nm, the concentration of 20.5 W %,dispersing medium: isopropanol, refractive index of the particles: 1.20,and a water content of 0.5 W % against an amount of SiO₂), 1.88 g ofγ-acrylo oxypropyl trimethoxysilane (produced by Shin-Etsu Silicone Co.,Ltd.: KBM-5103 with the SiO₂ content of 81.6%) was added to 100 g of thesol, and then a 28% ammonia aqueous solution was added to the mixturesolution so that the ammonia concentration would be 400 ppm against 100g of the organosol (the water content was 1 W % against the amount ofSiO₂). The mixture solution was agitated for 5 hours at 40° C. to obtaina sol in which surface-processed hollow microparticles were dispersed(with the solid phase concentration of 20.3%).

A weight loss of the surface-processed silica-based hollow microparticledispersion sol was measured by the TG-DTA (at a temperature in the rangefrom 200° C. to 500° C.) to find that the weight loss was 4.5%.

0.42 g of an optical initiator (produced by Chibus Specialities (Corp.):Irgacure 184 which is dissolved by IPA and have a solid phaseconcentration of 10%) and 57.08 g of a mixture solution of isopropanoland methyl isobutyl ketone (with the mixing ratio of 1/1) were mixedwith 15.5 g of the surface-processed silica-based hollow microparticledispersion sol, 24 g of perfluoroethyl acrylate (produced by KyoueishaKagaku Corp.: FA-108), and 3 g of diethylaminoethyl methacrylate(produced by Kyoueisha Kagaku Corp.: Light ester DE), and the mixturesolution was fully agitated to prepare a paint for forming a transparentcoating film (A-3).

[Preparation of a Transparent Film-Coated Substrate (3)] (HardCoat+Glare-Proof and Antireflection Properties)

The paint for forming a transparent coating film (A-3) was applied on aPET film (with the thickness of 100 μm, the refractive index of 1.65,the substrate transmittance of 88.0%, the haze of 1.0%, and thereflection coefficient of 5.1%) with a bar coater, and the applied paintwas died for 1 minute at 70° C. Then the dried paint was cured byirradiating light from a high pressure mercury lamp (80-W/cm) for 1minute to prepare a transparent film-coated substrate (3). A thicknessof the transparent film-coated substrate was 5 μm. A portion of thetransparent coating film was cut in a direction vertical to thelongitudinal direction, and the cross section was observed with atransmission electron microscope to find that the silica-based hollowmicroparticles form a layer with the thickness of 120 nm in the uppersection, and that only the matrix was present and no particle wasobserved in the lower section.

Example 16 Preparation of a Paint for Forming a Transparent, CoatingFilm (A-4)

A component with a low refractive index used in this example was a solin which silica-based hollow microparticles were dispersed (produced byCatalysts and Chemicals Industries Co., Ltd. Thrulya 1420 with theaverage particle diameter of 60 nm, the concentration of 20.5 W %,dispersing medium: isopropanol, refractive index of the particles: 1.30,and a water content of 0.5 W % against an amount of SiO₂), 10 g ofperfluorooctyl ethyl triethoxysilane (produced by Toray Dow CorningCorporation: AY43-158E 100%) was added to 100 g of the sol, and then a28% ammonia aqueous solution was added to the mixture solution so thatthe ammonia concentration would be 400 ppm against 100 g of theorganosol (the water content was 1 W % against the amount of SiO₂). Themixture solution was agitated for 5 hours at 40° C. to obtain a sol inwhich surface-processed hollow microparticles were dispersed (with thesolid phase concentration of 20.3%).

A weight loss of the surface-processed silica-based hollow microparticledispersion sol was measured by the TG-DTA (at a temperature in the rangefrom 200° C. to 500° C.) to find that the weight loss was 4.5%.

As a high refractive index component for prevention of electrification,an ATO microparticle dispersion sol (produced by Catalysts and ChemicalsIndustries Co., Ltd.: ELCOM V-3501 with the average particle diameter of8 nm, the concentration of 20.5 W %, a dispersing medium: ethanol, arefractive index of the particle: 1.75) was used. 0.15 g of γ-acrylooxypropyl trimethoxysilane (produced by Shin-Etsu Silicone Co., Ltd.:KBM-5103 with the SiO₂ content of 81.2%) was mixed in 100 g of this sol.Then 10 g of ultrapure water was added to the mixture, and the resultantmixture solution was agitated for 5 hours at 40° C. to obtain asurface-processed ATO microparticle dispersion sol (with the solid phasecontent of 20.0%).

A weight loss of the surface-processed ATO microparticle dispersion solwas measured (at a temperature in the range from 200° C. to 500° C.) tofind that the weight loss was 0.5%.

0.35 g of an optical initiator (produced by Chibus Specialities (Corp.):Irgacure 184 which is dissolved by IPA and have a solid phaseconcentration of 10%) and 27.15 g of a mixture solution of isopropanoland methyl isobutyl ketone (with the mixing ratio of 1/1) were mixedwith 15.5 g of the surface-processed silica-based hollow microparticledispersion sol, 30 g of the surface-processed ATO microparticledispersion sol, and 27 g of hexaerythrythol tripentaacrylate (producedby Nippon Kayaku Co., Ltd.: KAYARAD DPHA) to prepare a paint for forminga transparent coating film (A-4).

[Preparation of a Transparent Film-Coated Substrate (4)] (HardCoat+Prevention of Electrification and Reflection)

The paint for forming a transparent coating film (A-4) was applied on aTAC film (with the thickness of 80 μm, the refractive index of 1.48, thesubstrate transmittance of 88.0%, the haze of 0.0%, and the reflectioncoefficient of 4.8%) with a bar coater, and the applied paint was diedfor 1 minute at 70° C. Then the dried paint was cured by irradiatinglight from a high pressure mercury lamp (80-W/cm) for 1 minute toprepare a transparent film-coated substrate (4). A thickness of thetransparent film-coated substrate was 5 μm. A portion of the transparentcoating film was cut in a direction vertical to the longitudinaldirection, and the cross section was observed with a transmissionelectron microscope to find that the silica-based hollow microparticlesform a layer with the thickness of 100 nm in the upper section, and alsothat the ATO microparticles were present in the matrix in the lowersection.

Comparative Example 4 [Preparation of a Paint for Forming a TransparentCoating Film (R-1)]

A component with a low refractive index used in this example was a solin which silica-based hollow microparticles were dispersed (produced byCatalysts and Chemicals Industries Co., Ltd. Thrulya 1420 with theaverage particle diameter of 60 nm, the concentration of 20.5 W %,dispersing medium: isopropanol, refractive index of the particles: 1.30,and a water content of 0.5 W % against an amount of SiO₂), 1 g ofperfluorooctyl ethyl triethoxysilane (produced by Toray Dow CorningCorporation: AY43-158E 100%) was added to 100 g of the sol. The mixturesolution was agitated for 5 hours at 40° C. to obtain a sol in whichsurface-processed hollow microparticles were dispersed (with the solidphase concentration of 20.3%).

A weight loss of the surface-processed silica-based hollow microparticledispersion sol was measured by the TG-DTA (at a temperature in the rangefrom 200° C. to 500° C.) to find that the weight loss was 0.6%.

0.42 g of an optical initiator (produced by Chibus Specialities (Corp.):Irgacure 184 which is dissolved by IPA and have a solid phaseconcentration of 10%) and 62.04 g of a mixture solution of isopropanoland methyl isobutyl ketone (with the mixing ratio of 1/1) were mixedwith 10.54 g of the surface-processed silica-based hollow microparticledispersion sol, 24 g of pentaerythrythol triacetate (produced byKyoueisha Kagaku Corp.: PE-3A), and 3 g of diethylaminoethylmethacrylate (produced by Kyoueisha Kagaku Corp.: Light ester DE), andthe mixture solution was fully agitated to prepare a paint for forming atransparent coating film (R-1).

[Preparation of a Transparent Film-Coated Substrate (R-1)] (HardCoat+Prevention of Reflection)

The paint for forming a transparent coating film (R-1) was applied on aPET film (with the thickness of 100 μm, the refractive index of 1.65,the substrate transmittance of 88.0%, the haze of 1.0%, and thereflection coefficient of 5.1%) with a bar coater, and the applied paintwas died for 1 minute at 70° C. Then the dried paint was cured byirradiating light from a high pressure mercury lamp (80-W/cm) for 1minute to prepare a transparent film-coated substrate (R−1). A thicknessof the transparent film-coated substrate was 5 μm. A portion of thetransparent coating film was cut in a direction vertical to thelongitudinal direction, and the cross section was observed with atransmission electron microscope to find that the silica-based hollowmicroparticles are homogeneously dispersed in the film.

1-16. (canceled)
 17. A composition for forming a transparent coatingfilm comprising hollow silica microparticles and a binder, wherein thehollow silica microparticles have an average particle diameter of 5 to300 nm when measured by the dynamic light scattering method, a specificsurface area of 50 to 1500 m²/g, and also having an outer shell in whichcavities are formed, wherein the microparticles lose weight by 1.0 W %or more at a temperature in the range of from 200° C. to 500° C. whenmeasured by the thermogravimetry (TG), and wherein a surface charge (QA)of the hollow silica microparticles contained in the compositions forforming a transparent coating film is in the range from 5 to 20 μeq/g.18. The composition for forming a transparent coating film according toclaim 17, wherein the microparticles have a positive DTA peak whenmeasured by the differential thermogravimetric analysis (DTA) at atemperature in the range from 200° C. to 500° C.
 19. The composition forforming a transparent coating film according to claim 17, wherein thehollow silica microparticles have an organic group directly bonded to asilicon atom on a surface thereof.
 20. The composition for forming atransparent coating film according to claim 19, wherein the organicgroup is at least one selected from the group consisting of saturated orunsaturated hydrocarbon groups having 1 to 18 carbon atoms andhalogenated hydrocarbon groups having 1 to 18 carbon atoms.
 21. Thecomposition for forming a transparent coating film according to claim17, wherein a concentration (C_(PA)) of the hollow silica microparticlescontained in the composition for forming a transparent coating film isin the range from 0.1 to 20 W %, a concentration (C_(M)) of the binderas a solid component is in the range from 1 to 50 W %, and a solvent isa polar one.
 22. The composition for forming a transparent coating filmaccording to claim 17, wherein the composition for forming a transparentcoating film containing the hollow silica microparticles with thesurface charge (Q_(A)) in the range from 5 to 20 μeq/g also containsmetal oxide microparticles with a surface charge (Q_(B)) in the rangefrom 51 to 150 μeq/g, and wherein a value of difference between thesurface charge (Q_(B)) of the metal oxide microparticles and the surfacecharge (Q_(A)) of the hollow silica microparticles [(Q_(B))−(QA)] is inthe range from 20 to 100 μeq/g.
 23. The composition for forming atransparent coating film according to claim 22, wherein a concentration(C_(PA)) of the hollow silica microparticles contained in thecomposition for forming a transparent coating film is in the range from0.1 to 20 W %, a concentration (C_(PB)) of the metal oxidemicroparticles is in the range from 0.1 to 20 W %, a concentration(C_(M)) of the binder as a solid component is in the range from 1 to 50W %, and a solvent is a polar one.
 24. The composition for forming atransparent coating film according to claim 18, wherein the hollowsilica microparticles have an organic group directly bonded to a siliconatom on a surface thereof.
 25. The composition for forming a transparentcoating film according to claim 24, wherein the organic group is atleast one selected from the group consisting of saturated or unsaturatedhydrocarbon groups having 1 to 18 carbon atoms and halogenatedhydrocarbon groups having 1 to 18 carbon atoms.
 26. The composition forforming a transparent coating film according to claim 18, wherein aconcentration (C_(PA)) of the hollow silica microparticles contained inthe composition for forming a transparent coating film is in the rangefrom 0.1 to 20 W %, a concentration (C_(M)) of the binder as a solidcomponent is in the range from 1 to 50 W %, and a solvent is a polarone.
 27. The composition for forming a transparent coating filmaccording to claim 18, wherein the composition for forming a transparentcoating film containing the hollow silica microparticles with thesurface charge (Q_(A)) in the range from 5 to 20 μeq/g also containsmetal oxide microparticles with a surface charge (Q_(B)) in the rangefrom 51 to 150 μeq/g, and wherein a value of difference between thesurface charge (Q_(B)) of the metal oxide microparticles and the surfacecharge (Q_(A)) of the hollow silica microparticles [(Q_(B))−(Q_(A))] isin the range from 20 to 100 μeq/g.
 28. The composition for forming atransparent coating film according to claim 27, wherein a concentration(C_(PA)) of the hollow silica microparticles contained in thecomposition for forming a transparent coating film is in the range from0.1 to 20 W %, a concentration (C_(PB)) of the metal oxidemicroparticles is in the range from 0.1 to 20 W %, a concentration(C_(M)) of the binder as a solid Component is in the range from 1 to 50W %, and a solvent is a polar one.